I hate to dredge up an old post but the relevance and lack of SME input in other related posts isn't cutting it.
I recently bought a 3rd RMR Type 2 and this one has way more Parallax Shift Relative To Head Position then my other two RMRs.
I keep hearing this "works fine for me" or "Cool guys uses brand ________ so it must be perfect" but that just shows a lack of exposure to the conditions that cause the error in the first place.
If you shoot in a flat, 2D environment with stationary targets and can assume an ideal firing position and grip every time you pull the trigger you'll never notice that your dot moves all over the damned place relative to your head position. However if you train in a 3 dimensional environment and practice things like firing from a ladder, laying flat on your back, prone, weak hand "wounded", from inside a vehicle, underneath a vehicle or in some other cramped area where you can't extend your arms fully the parallax shift thing becomes a real PITA.
I was an early adopter of the Aimpoint T1 and have kept the same 4moa T1 turned on almost continuously since GW Bush was president other than an annual battery change. I've done some great shooting with that little T1 equipped Colt over the years and I'd still bet my life on that setup BUT when doing headshots in a CQB range scenario I can definitely miss the badguy by 3-5 inches or worse yet hit the hostage part of the target if my face comes off the stock even a little bit because I'm in an unorthodox shooting position.
Reducing/Eliminating Parallax Shift Relative To Head Position needs to become a top priority of RDS manufacturers who cater to the defense, law enforcement and personal defense segments of the market but it requires someone other than just the Green Eye Tactical guy to get their attention and the only guy making a concerted albeit unscientific attempt at including Parallax Shift in his optic reviews/tests is a youtuber called JRR Armory. I wish he would adopt the Green Eye Tactical targets and method of assessing this but something is better than nothing I guess..
https://www.youtube.com/user/jobane2...query=parallax
Someone needs to go beyond what dopushups has done and make a master list of every RDS type optic in the market ranked by how much of this PARALLAX SHIFT RELATIVE TO HEAD POSITION is present in each optic at common shooting distances(5, 15, 25, 50, 75 and 100 meters/yards so end users can get an idea of what their pistol or carbine will shoot like when laying on their side trying to shoot under a car or kneeling at a range barricade with a slot that's just a hair too tall to achieve a "perfect" kneeling position .